The present invention relates to a hybrid transmission for a motor vehicle, comprising a main gearbox, which is made as a mechanical gearbox with a plurality of gear ratios and is adapted to be connected to a drive shaft of the internal combustion engine of the vehicle, and a single electric machine which is connected to the main gearbox so as to assist the internal combustion engine of the vehicle in producing the driving torque to be transmitted to the vehicle wheels.
Hybrid transmissions for motor vehicles, both of the single-clutch type and of the double-clutch type, are known, in which the electric machine is permanently connected or selectively connectable to a primary shaft or to a secondary shaft of the main gearbox so as to be able to transmit torque to that shaft or receive torque from that shaft. The electric machine is thus able to perform not only the main functions of traction (generation of mechanical power for the vehicle wheels by taking energy from the batteries of the vehicle) and of regeneration (generation of electrical power for the batteries of the vehicle by recovering the kinetic energy of the vehicle or by exploiting the internal combustion engine when it runs with the vehicle being stationary), but also auxiliary functions such as for example the functions of alternator and of starting motor.
EP-A-1 232 891 discloses a hybrid transmission for a motor vehicle, comprising a main gearbox and a single electric machine, wherein the main gearbox is a mechanical gearbox with a plurality of gears and comprises at least one primary shaft adapted to be connected to a drive shaft of the internal combustion engine of the vehicle, and at least one secondary shaft adapted to be connected to the vehicle wheels. The electric machine is releasably connected both to the at least one primary shaft and to the at least one secondary shaft by means of a connection gear set, which includes a first gearwheel idly mounted on the at least one primary shaft and a second gearwheel idly mounted on the at least one secondary shaft and directly or indirectly meshing with the first gearwheel, so as to allow the transmission of the torque between the electric machine and the at least one primary and secondary shafts. The transmission further comprises a first coupling device interposed between the electric machine and the at least one primary shaft to control the connection between the electric machine and this shaft, and a second coupling device interposed between the electric machine and the at least one secondary shaft to control the connection between the electric machine and this shaft. The first coupling device is shiftable into an engaged position, in which it connects the first gearwheel for rotation with the respective primary shaft, and into a disengaged position, in which it disconnects the first gearwheel from the respective primary shaft. The second coupling device is shiftable at least into an engaged position, in which it connects the second gearwheel for rotation with the respective secondary shaft, and into a disengaged position, in which it disconnects the second gearwheel from the respective secondary shaft, in such a manner that with the first coupling device in the engaged position the electric machine is able to transmit torque to the primary shaft on which the first gearwheel is mounted, while with the second coupling device in the engaged position the electric machine is able to transmit torque to the secondary shaft on which the second gearwheel is mounted.